Rigid polyurethanes are generally prepared by the reaction of a polyfunctional hydroxy compound, preferably one with a functionality of 3 or greater, with a polyfunctional isocyanate, preferably one having a functionality of 2.5 or more. In the manufacture of such rigid polyurethane foams, the polyfunctional isocyanate is typically admixed with a liquid stream comprising a polyhydroxy material, a blowing agent, a surfactant for stabilizing cell-size, and a catalyst. The rigid foam can be produced by either a "one-shot" method or by employing a semi-prepolymer or a prepolymer method. In the so-called "one-shot" method, a first stream of reactant containing isocyanate and/or polyisocyanate is admixed with a second stream comprising a polyol, a surfactant, and a blowing agent. Generally the second stream also contains a catalyst. Typically, in the manufacture of urethane board insulating stock, the resulting admixture is discharged into a moving conveyor provided with physical restraint elements, and the chemical reaction immediately commences, generating an exotherm, and the exotherm causes the vaporization of the volatile blowing agent if one is used. It is crucial, in the manufacture of insulating board stock to balance the reactivity and quantity of the respective components so that the exotherm, although great enough to cause the vaporization of the blowing agent, is not great enough to cause the disintegration of the cellular character of the resulting foam. Also, as the molecular weight builds, the viscosity of the reactant mixture increases, and this factor plus the presence of a surfactant e.g. cell wall stabilizer, assists in maintaining the closed cell structure of the resulting foam.
The fire retardant or, "low fire hazard" properties of furan ring-containing materials is well known due to the self-extinguishing property of the char which forms when furan-containing materials are burned. The disclosure in U.S. Pat. No. 4,029,611 issued to Cenker et al. shows a rigid cellular foam having carbodiimide and isocyanurate linkages prepared by catalytically condensing an organic polyisocyanate in the presence of a carbodiimide-promoting catalyst, a trimerization catalyst, and a polyfurfuryl alcohol polymer. The resulting isocyanurate foam has improved flame retardancy. The polyfurfuryl alcohol polymer employed includes the condensation products of furfuryl alcohol with formaldehyde, furfural, urea or mixtures thereof, produced by reaction in the presence of an acid catalyst providing a pH of 1 to 4, preferably 1.5 to 3, at a temperature of 25.degree. C. to 120.degree. C.
Likewise, a U.S. Pat. No. 3,865,757 issued to Wade teaches "resinous foam" produced by reaction of a furan compound, an isocyanate compound, and a phosphorus-containing inorganic acid or complex thereof. The reaction mixture disclosed can also contain an alcohol, an amine, a surfactant, and/or a supplementary blowing agent.
In addition, other now conventional low flame hazard polyurethane foams achieving a rating of Class I flame hazard rating according to the ASBM E-84 Steiner tunnel test are also well known. One of these well known non-furan-containing rigid insulating foams are produced by typical "standard" methods and is described hereinafter in Test "A" in Example 1.
An object of this invention is to provide a rigid urethane foam exhibiting low flame hazard properties.
A further object of this invention is to provide a self-extinguishing furan-containing urethane foam.
A still further object of this invention is to provide a furan-containing rigid urethane insulating foam having a closed cell content greater than 80%.
Another object of this invention is to provide a stable furan-containing polyol mixture composition for producing a rigid urethane foam, such mixtures having a Freon compatibility greater than 30 parts Freon to 100 parts of furan-containing polyol mixture.
Yet another object of this invention is to provide a rigid urethane foam having a compressive strength greater than 30 psi and a friability of less than 20%, which characteristics substantially exceed the performance that is believed to be achieved in the manufacture of present-day industry "standard" foams.